EP3283559B1 - Thermally and/or electrically conductive materials and method for the production thereof - Google Patents

Description

The invention relates to the field of polymeric materials with a very high filler rate and controlled porosity. It relates in particular to the field of materials with a very high rate of thermal conductive and / or electrically conductive charges. It relates to a method of manufacturing a porous polymeric material comprising a high filler rate. The invention also relates to the polymeric compositions and the materials obtained by these methods, as well as their uses.

State of the prior art

Materials with high thermal conductivity are used in different applications. They are mainly found in appliances and devices in which heat is generated, where they are used to evacuate heat to the outside, in order to avoid a continuous rise in temperature and deterioration of such equipment.

For example, devices using semiconductors, such as computers, transistors, LEDs, produce heat during their operation and the efficiency of the electronic parts that compose them can be degraded by this heat formation. It is known to use parts of thermally conductive materials to remove the heat formed inside these devices.

In electronic applications in particular, the surface of the heat-generating components is rarely flat and it is preferred to use a conformable material, capable of adapting to the shapes of the elements between which it is placed so as to optimize the contact between the thermally conductive material. and the heat-producing element, so that the heat flow is facilitated. In certain applications such as buildings, where large parts of thermally conductive material are used, the aim is to minimize the density of these materials, in particular for reasons of workability. In the aeronautical field, attempts are also made to minimize the density of on-board elements, in particular electronic components, which incorporate heat sinks made of thermally conductive material.

Also thermal conductive materials must have high thermal conductivity, but also, depending on the applications: high conformability, reduced density.

Polymeric materials with high electrical conductivity are used in different applications. They are mainly found in the manufacture of cables electrical, in coatings intended for electromagnetic shielding, antistatic protection, anti-lightning coatings.

Such materials, depending on their uses, must have a certain flexibility (electric cables), be able to adapt to the contours of rigid parts of irregular shape, and be sufficiently light, for applications in aeronautics in particular.

Also electrically conductive materials must have high electrical conductivity, but also, depending on the applications: high flexibility, high conformability, reduced density.

Usually, to produce a thermally conductive material or an electrically conductive material, thermal conductive charges, respectively electric conductors, are added to a polymer matrix. The thermal or electrical conductivity of the composite resulting from this mixture depends mainly on the type and nature of the conductive fillers used, but also on the quantity of these fillers present in the material. In fact, the matrix serves mainly to ensure cohesion of these charges and generally does not itself have thermal or electrical conductor properties. Thus, the higher the quantity of thermal conductive or electrically conductive charges present in the composite, the higher the overall thermal conductivity, respectively electrical, of the material obtained. However, the incorporation of fillers in high amounts into a polymer matrix is not without difficulties.

The more fillers are introduced into a polymer matrix, the higher the viscosity of the mixture, and the more difficult it is to transform the mixture efficiently by the usual plastics processing methods. This problem has been solved in different ways in the prior art: by the incorporation of fillers in limited quantities into the final composite, which also limits the conductivity obtained, by the use of low viscous polymer precursors which are then crosslinked, or by the use of a binder polymer in solution in a solvent which is then evaporated.

Thus the document US6306957 describes polymeric compositions comprising up to 90% by volume of thermal conductive fillers. These compositions are based on silicone precursors of low molar masses mixed with the thermal conductive fillers. The precursor is then crosslinked to ensure the strength of the final composite.

US2012 / 0025131 describes a polymeric composition comprising thermal conductive or electrically conductive fillers. This composition is prepared from a liquid polymeric composition which may be composed of precursors reagents of the epoxy resin, urethane or silicone type subsequently crosslinked, or of a solution of a thermoplastic polymer dispersed in a solvent. The mass rate of charges is not specified.

The preparation of a thermally conductive material by the solvent route presents problems of storage, handling and recycling of large quantities of solvents, in particular if organic solvents are used, such a process has drawbacks from an environmental and health standpoint. . The manufacture of a polymeric composite material by the solvent route optionally makes it possible to obtain a porous material, the porosity of which is difficult to control. In particular, obtaining a porosity of controlled size or a continuous porosity is difficult to control. Further, only thin films (a few micrometers thick) can be produced by this route.

A thermally conductive material prepared from precursors which are then crosslinked is neither convertible nor recyclable. Furthermore, the variety of polymeric bases which can be employed in these processes is limited and the process times are long. This type of process does not make it possible to obtain a porous material. Finally, such materials are not very conformable and therefore of limited interest in certain applications.

WO2005 / 071001 describes thermoplastic compositions of the PET or PBT type with high molar masses comprising a thermally conductive filler, calcium fluoride. The composition is prepared by the melt route. Mass percentages of conductive fillers of up to 70% are described.

WO2006 / 023860 also mentions the production by melt of thermoplastic compositions comprising up to 80% by weight of a boron nitride of particular shape without this possibility being illustrated by examples. The implementation of the process includes the use of an oil, it is not a thermoplastic transformation process.

US2010 / 0204380 , WO2009 / 064883 and WO2009 / 115512 describe a molten process making it possible to obtain a thermally conductive composite. The volume rates of thermal conductive fillers indicated are respectively 70%, 75% and 70%, however, the embodiments show significantly lower levels of fillers.

WO2012 / 000935 describes thermoplastic compositions comprising up to 60% by mass of thermal conductive fillers. US2011 / 0040007 describes the production of a thermally conductive composite based on a thermoplastic polymer having a maximum of 76% by volume of filler.

The implementation of the manufacturing processes described in these documents is made difficult by high loading rates. In addition, the materials obtained are not porous.

To remedy these drawbacks, US2011 / 009544 describes a thermoplastic-based thermally conductive composite obtained by the melt process with thermally conductive fillers functionalized at the surface. The fillers are functionalized by silane groups which allow their incorporation in high amounts. However, this solution has the drawback of requiring the manufacture of functionalized fillers, which represents an additional cost for the material.

It has been observed that the levels of conductive fillers achievable in the molten process with conventional polymers and ungrafted mineral or carbon fillers are, to date, less than 80% by volume. And such charge rates have only been obtained with certain polymers, but conventional melt processes do not make it possible to achieve a high charge rate with any type of polymer. For example, polyacrylonitrile co-methyl acrylate is known to be difficult to melt processable when it is pure, so adding 70% by volume filler to this material is remarkable. In addition, the melt processes of the prior art result in a dense non-porous composite.

The document US7820328 describes an electrode material comprising a polymeric binder and a conductive filler in a proportion of less than 10% by mass. This material is obtained by using a small amount of a sacrificial polymer (at most 5% by mass) which is then thermally decomposed to obtain the electrode with a weakly porous nature. This necessarily results in reduced porosity. However, the process followed is not explicitly described, it is carried out in the presence of a solvent or by pressing a powder, so as to form a coating film on a current collector. The material is intended for an application different from that of the invention, a minor part of the charges used are electrically conductive. No exemplary embodiment illustrates the implementation of a process or the characterization of a product.

The document US2008 / 0226984 discloses an electrode material comprising a polymeric binder and a high proportion conductive filler. This material is obtained by using a small amount of a sacrificial polymer which is then thermally decomposed to obtain the electrode. The process implemented involves the use of a solvent. The material is intended for an application different from that of the invention, the charges used are electrical conductors but not thermal, and the application requires only low electrical conductivity.

In these two documents, the process results in electrode materials in the form of thin films (approximately 20 μm). The use of small amounts of sacrificial material and of a process by the solvent route or by powder pressing does not make it possible to control the size or the continuity of the porosity.

The document FR 2 759 089 describes a porous composite material with a high specific surface area and its preparation process which uses a sacrificial polymer phase and fillers with a high specific surface area. The soluble or calcinable polymers are not eliminated in their entirety because of their affinity for the fillers chosen, in particular activated carbon. It is observed that there remains in the composite material more than 20% by mass of these sacrificial polymers.

The document US-7,820,328 described: an electrode material obtained from a mixture of a binder polymer, a sacrificial polymer and electrically conductive charges. The process is carried out by solvent route or by powder compression and uses only 1 to 5% of sacrificial polymer. It cannot lead to a self-supporting material.

The objective of the invention has been to overcome the problems encountered when using the thermally conductive polymeric compositions of the prior art. In particular, attempts have been made to develop materials which are prepared by the molten route, without solvent, which are recyclable and which incorporate high amounts of thermal conductive charges and / or of electrically conductive charges. An attempt has been made to develop a process which can be implemented with mineral fillers or carbonaceous fillers without a functionalization step of these fillers being necessary. A method has been implemented which makes it possible to obtain a self-supporting material, that is to say a material which is not necessarily in the form of a coating applied to a support. In particular, materials have been obtained which have both sufficient thickness and cohesion to be self-supporting. When the materials of the invention are in the form of a coating, the method of the invention makes it possible to obtain materials having a thickness greater than that of the materials of the prior art.

An attempt has also been made to implement a method which results in a porous material so as to be able to obtain a material with a lower density compared to the methods of the prior art. We have also sought to obtain a material which is conformable.

Summary of the invention

• les charges conductrices thermiques présentant une conductivité thermique supérieure ou égale à 5 W/mK, et les charges conductrices électriques présentant une résistivité inférieure ou égale à 0.1 Ohm.cm,
• les charges (B) représentant au moins 75%, avantageusement au moins 80% en masse par rapport à la somme des masses de la phase polymérique (A) et des charges (B), ce procédé comprenant les étapes suivantes :
  1. a) Mélangeage à chaud par voie fondue de la phase polymérique (A), des charges (B), et d'une phase polymérique sacrificielle (C), de façon à obtenir un mélange,
  2. b) Mise en forme du mélange,
  3. c) Elimination de la phase polymérique sacrificielle,
• et la phase polymérique sacrificielle (C) représente au moins 15 % en masse de la masse totale du mélange de l'étape a).

A first object of the invention is a process for preparing a porous composite material comprising at least (A) a polymeric phase forming a binder and (B) one or more fillers chosen from:

• thermal conductive loads having a thermal conductivity greater than or equal to 5 W / mK, and electrically conductive loads having a resistivity less than or equal to 0.1 Ohm.cm,
• the fillers (B) representing at least 75%, advantageously at least 80% by mass relative to the sum of the masses of the polymer phase (A) and of the fillers (B), this process comprising the following steps:
  1. a) Hot melt mixing of the polymer phase (A), of the fillers (B), and of a sacrificial polymer phase (C), so as to obtain a mixture,
  2. b) Shaping of the mixture,
  3. c) Elimination of the sacrificial polymeric phase,
• and the sacrificial polymeric phase (C) represents at least 15% by mass of the total mass of the mixture of step a).

According to a preferred embodiment, the porous composite material comprises, by mass relative to the total mass of the material, from 0 to 5% of one or more decomposition residues of the sacrificial phase.

According to a preferred embodiment, the sacrificial polymeric phase (C) represents from 20 to 80% by mass of the total mass of the mixture of step a).

According to a preferred embodiment, step a) is carried out in an internal mixer or in an extruder.

According to a preferred embodiment, step c) is carried out by thermal decomposition of the sacrificial polymer phase.

According to a preferred embodiment, the sacrificial polymer phase is based on at least one polymer chosen from polyalkene carbonates, preferably from polyethylene carbonates and polypropylene carbonates.

According to a preferred embodiment, the polymeric phase forming a binder is based on at least one polymer chosen from: thermoplastics, elastomers, thermoplastic elastomers, advantageously from: polyacrylonitrile, polyolefins, halogenated polymers, acrylic polymers , acrylates, methacrylates, vinyl acetates, polyethers, polyesters, polyamides, aromatic polymers, hydrogenated acrylonitrile-butadiene, copolymers of ethylene and of an alkyl acrylate, polyisoprene, rubbers.

According to a first preferred variant, the fillers are chosen from: aluminum nitride, boron nitride, magnesium and silicon nitride, silicon carbide, diamond, and mixtures thereof.

According to a second preferred variant, the fillers are chosen from: graphite, graphene, carbon nanotubes (CNT), carbon black, metallic fillers such as aluminum, copper or silver and their mixtures.

According to a preferred embodiment, step b) comprises shaping in the form of a film.

According to a preferred embodiment, the method further comprises at the end of step c) a step d) of compression.

• 3 à 25 % d'au moins un polymère choisi parmi les polymères thermoplastiques, les élastomères et les thermoplastiques élastomères,
• 75 à 97 % d'au moins une charge choisie parmi les charges conductrices thermiques présentant une conductivité thermique supérieure ou égale à 5 W/mK, et les charges conductrices électriques présentant une résistivité inférieure ou égale à 0,1 Ohm.cm,
• 0 à 5 % d'un ou plusieurs additifs ou résidus de décomposition de la phase sacrificielle.

A further subject of the invention is a porous composite material capable of being obtained by the process described in summary above, and in more detail below, which has the following composition, by mass relative to the total mass of the product. material :

• 3 to 25% of at least one polymer chosen from thermoplastic polymers, elastomers and elastomeric thermoplastics,
• 75 to 97% of at least one load chosen from thermal conductive loads having a thermal conductivity greater than or equal to 5 W / mK, and electrically conductive loads having a resistivity less than or equal to 0.1 Ohm.cm,
• 0 to 5% of one or more additives or decomposition residues of the sacrificial phase.

According to a preferred embodiment, the material is chosen from a self-supporting material and a coating with a thickness greater than or equal to 250 μm.

According to a preferred embodiment, the material is capable of being obtained by a process for preparing a porous composite material, further comprising at the end of step c) a step d) of compression, this material comprising a polymer matrix based on a polymer chosen from thermoplastic polymers, elastomers and elastomeric thermoplastics, thermally conductive fillers, and exhibiting thermal conductivity in at least one direction greater than or equal to 15 W / mK

1. (A) une phase polymérique à base de polymères choisis parmi les polymères thermoplastiques, les élastomères et les thermoplastiques élastomères,
2. (B) une ou plusieurs charges choisies parmi les charges conductrices thermiques présentant une conductivité thermique supérieure ou égale à 5 W/mK, et les charges conductrices électriques présentant une résistivité inférieure ou égale à 0,1 Ohm.cm,
3. (C) une phase polymérique sacrificielle,

la ou les charges (B) représentant au moins 75%, avantageusement au moins 80% en masse par rapport à la somme des masses du polymère (A) et des charges (B), la phase polymérique sacrificielle (C) représentant au moins 15 % en masse par rapport à la somme des masses de (A), (B) et (C).A subject of the invention is also a polymer composition capable of being obtained at the end of step a) or of step b) of the process for preparing a porous composite material, this composition comprising at least:

1. (A) a polymer phase based on polymers chosen from thermoplastic polymers, elastomers and thermoplastic elastomers,
2. (B) one or more loads chosen from thermal conductive loads having a thermal conductivity greater than or equal to 5 W / mK, and electrically conductive loads having a resistivity less than or equal to 0.1 Ohm.cm,
3. (C) a sacrificial polymeric phase,

the fillers (B) representing at least 75%, advantageously at least 80% by mass relative to the sum of the masses of the polymer (A) and of the fillers (B), the sacrificial polymer phase (C) representing at least 15 % by mass with respect to the sum of the masses of (A), (B) and (C).

A further subject of the invention is a method of manufacturing a porous carbonaceous material which is thermally conductive and / or electrically conductive, this method comprising the implementation of the method for preparing a porous composite material and further comprising at the end of this process at least one step e) of pyrolysis or graphitization.

detailed description

This result was obtained by means of a method making it possible to incorporate, directly in the molten process and by conventional plastic transformation methods, very high rates of thermal conductive and / or electrically conductive mineral or carbon fillers, greater than 80%. by mass in the final material. This process makes it possible to obtain a porous material and to control the porosity within the final product. This result is obtained by using a polymer phase, which forms the binder of the final material, in combination with a sacrificial phase. The composition is chosen with regard to the manufacturing process used and the final application of the material. The method of the invention also makes it possible to orient the loads with a form factor, based on the implementation parameters and, where appropriate, on an additional recompression step. The process of the invention has made it possible to produce thermally conductive and / or conductive materials in the molten process. electrics which contain a rate of mineral or carbonaceous charges greater than 80% by mass without first modifying the surface of the charges or using a coupling agent or solvent, these materials being usable as they are.

The mixing, the dispersion and the homogeneous distribution of the binder polymer and of the sacrificial phase and of the various mineral or carbonaceous fillers are ensured by the implementation of the molten process. A possible pyrolysis or graphitization of the binder polymer is possible in a second step in order to optimize the performance, depending on the envisaged application. The control of the porosity in terms of size, volume and morphology is ensured by the control of the mixing parameters (screw profile, etc.) during the implementation of the process. Secondly, the material can be subjected to a compression step which leads to a reduction in the pore volume. The control of the porosity is adapted according to the envisaged application.

In the present description, the expression “polymer” denotes both homopolymers and copolymers. It includes mixtures of polymers, oligomers, mixtures of monomers, oligomers and polymers.

The expression "consists essentially of" followed by one or more characteristics, means that may be included in the process or the material of the invention, in addition to the components or steps explicitly listed, components or steps which do not significantly modify the properties and characteristics of the invention.

- The polymeric phase forming a binder:

The material of the invention consists in particular of a polymer phase forming a binder and ensuring its cohesion. The polymeric phase can be of any kind provided that it can be transformed by the molten route and that it is compatible with the sacrificial phase chosen.

The polymeric phase forming a binder advantageously has a lower melting point of at least 20 ° C. relative to the decomposition temperature of the sacrificial phase so as to allow the mixture to be melted down. The binder-forming polymer phase is solid at room temperature (around 20-25 ° C) since it must be able to be shaped and will constitute the binder of the final material.

The compatibility between the binder-forming polymeric phase and the sacrificial polymeric phase is evaluated in a manner well known to those skilled in the art by mixing the materials by the molten route and by observing whether a phase separation occurs or whether the mixing occurs. is substantially homogeneous. To implement the process and obtain a satisfactory material, it is necessary to avoid macroseparation of phase between the binder polymer and the sacrificial polymer during processing, macroseparation which would result in the presence of a pure non-dispersed polymer phase of size greater than a few tens of μm.

For the production of this mixture, various parameters make it possible, in a well-known manner, to modulate the compatibility between the two phases. We can cite for example and without limitation: choice of equipment, such as screw profile; proportion of phases; compatibilizing agent. We can refer to a general work like: " Mixing and Compounding of Polymers Theory and Practice ", 2nd edition, Ica Edition, Manas-Zloczower , which describes in detail the main knowledge of polymer blending.

The choice of the two phases makes it possible to control the implementation of the process, but also the properties of the final material, such as its integrity, its porosity, its conformability.

The nature of the material which constitutes the polymeric phase forming the binder is chosen as a function of the final properties expected of the material, such as for example its plasticity and its mechanical properties.

According to one embodiment of the invention, pyrolyzable and / or graphitizable polymers are used in the polymeric phase forming the binder. After an additional pyrolysis or graphitization step, these polymers make it possible to obtain materials with a carbon structure endowed with thermal and / or electrical conductivity.

The polymeric phase forming binder comprises polymers and optionally additives. Preferably, the polymers represent at least 75% by mass of the polymeric phase forming the binder, advantageously at least 90%.

Advantageously, the polymers used in the process of the invention and entering into the composition of the final material (before possible pyrolysis or graphitization) are chosen from: thermoplastics, elastomers and elastomeric thermoplastics. Mention may be made, for example: polyacrylonitrile, polyolefins, halogenated polymers, acrylic polymers, acrylates, methacrylates, vinyl acetates, polyethers, polyesters, polyamides, aromatic polymers or else elastomeric polymers such as for example elastomeric polymers. hydrogenated acrylonitrile-butadiene (HNBR), copolymers of ethylene and an alkyl acrylate, polyisoprene or other rubbers.

Advantageously, the polymeric phase forming binder is based on at least one polymer chosen from: thermoplastics, elastomers, thermoplastic elastomers, which means that thermoplastic polymers, elastomers and the elastomeric thermoplastics represent at least 95% by mass of the polymers of the polymeric phase forming the binder, advantageously at least 98%.

According to a preferred embodiment of the invention, the polymeric phase forming binder comprises at least 50%, preferably at least 90%, even better, at least 95% by mass of at least one polymer chosen from polyacrylonitrile, hydrogenated acrylonitrile-butadiene and mixtures thereof.

Among the additives capable of being used in the polymer phase forming a binder, mention may be made of additives which are chosen for their function in the final material, for example: agents improving the resistance to fire or to oxidation or else crosslinking agents, such as bifunctional organic compounds, organic peroxides or sulfur compounds (for crosslinking rubbers), co-agents such as tri-allyl cyanurate. The use of these additives is useful without being necessary for the invention and depends directly on the intended application.

- The sacrificial polymer phase:

The sacrificial polymeric phase is composed of materials which have the property of decomposing during the application of a selected external stress, such as, for example, by raising the temperature or by dissolving in a solvent. The elimination or extraction of the sacrificial phase must be able to be carried out without impacting the rest of the material. It is preferable to use as the sacrificial material a compound which leaves little or no residue upon decomposition.

Advantageously, the sacrificial polymeric phase is solid at room temperature (around 20-25 ° C.) so as to allow the composition to be shaped.

Preferably, a sacrificial phase is chosen which can be extracted by thermal decomposition, and polymers having a clear degradation temperature known from the literature are preferred, while ensuring that the degradation temperature of the sacrificial phase is less than minus 20 ° C relative to the degradation temperature of the polymer (s) chosen for the polymer phase forming binder. Among the polymers capable of being removed by raising the temperature, mention may be made of polyalkene carbonates, such as, for example, polyethylene carbonates and polypropylene carbonates. Generally, these materials have the advantage of decomposing with moderate or no volume expansion. Thus, the volume of the shaped part is not or only slightly affected by the decomposition step of the sacrificial phase. In the presence of certain fillers such as graphite, the use of polyalkene carbonates can nevertheless sometimes lead to volume expansion. To improve the fluidity of the intermediate polymeric material and facilitate the implementation of the process, in a manner known to those skilled in the art, it is possible to use a mixture of polyalkene carbonates of different molar masses.

According to another embodiment, the sacrificial polymer phase can be extracted with a solvent and is based on at least one sacrificial polymer which can be extracted by liquid, preferably chosen from: polyethylene glycols, polypropylene glycols and their mixtures.

The sacrificial polymeric phase comprises polymers and optionally additives. Preferably, the polymers represent at least 95% by mass of the sacrificial polymeric phase, advantageously at least 98%.

Advantageously, the sacrificial polymeric phase is based on at least one polymer chosen from polyalkene carbonates, which means that the polyalkene carbonates represent at least 95% by mass of the sacrificial polymer phase, advantageously at least 98%.

According to a preferred embodiment of the invention, the polyethylene carbonates and the polypropylene carbonates represent at least 95% by mass of the sacrificial polymer phase, advantageously at least 98%.

Among the additives capable of being used in the sacrificial polymer phase, mention may be made of photoacid generators which act as additives to aid the decomposition of the sacrificial phases. Such products are described in Cupta M., Jayachandran P., Khol P., Photoacid generators for catalytic decomposition of polycarbonate, Journal of applied polymer science, 2007, Vol. 105, p.2655-2662 , for polypropylene carbonate for example. The use of these photoacids in the sacrificial polymer phase makes it possible to reduce the degradation temperatures. They are therefore useful without being necessary for the invention.

- The charges:

Depending on the expected properties of the composite polymeric material, thermal conductive charges, electrically conductive charges or charges having both properties are used.

Thermal conductive charges:

According to a first embodiment of the invention, thermal conductive fillers are used in the method and the composite material of the invention. The thermally conductive filler is chosen from those having a thermal conductivity greater than or equal to 5 W / mK.

The intrinsic thermal conductivity of known loads is described for example in " Thermal conductivity of Nonmetallic Solids, "YS Touloukian, RW Powell, CY Ho, and PG Klemans, IFI / Plenum: New York-Washington, 1970 or in " Thermal Conductivity-Theory, Properties and Applications, "TM Tritt, Ed., Kluwer Academic / Plenum Publishers: New York, 2004 .

Preferably, the thermally conductive filler has an intrinsic thermal conductivity greater than or equal to 10 W / mK, more preferably greater than or equal to 25 W / mK, advantageously greater than or equal to 50 W / mK.

Thermally conductive fillers which can be implemented in the invention are for example: AIN (aluminum nitride), BN (boron nitride), MgSiN2 (magnesium and silicon nitride), SiC (silicon carbide), graphite, graphene, carbon nanotubes (CNT), carbon nanofibers, carbon black, diamond, metallic fillers like aluminum, copper or silver or a combination of these.

It should be noted that some of these fillers, such as metallic fillers, graphite, graphene, carbon nanotubes (CNT), carbon nanofibers, carbon black, can also be electrically conductive. When it is desired to obtain an electrically insulating material, the use of such charges is avoided. In this case, use is preferably made of a filler having a resistivity greater than or equal to 10 ³ Ohm.cm, such as aluminum nitride, boron nitride, magnesium and silicon nitride or silicon carbide.

Electrically conductive charges:

The electrically conductive load is chosen from those having a resistivity less than or equal to 0.1 Ohm.cm.

Electrically conductive charges which can be implemented in the method and the material of the invention are for example: graphite, graphene, carbon nanotubes (CNT), carbon nanofibers, carbon black, fillers metallic such as aluminum, copper or silver, or a combination thereof.

- Additives:

In addition to the additives intended to modify the properties of the final material, in particular before pyrolysis, and those intended to facilitate the elimination of the sacrificial phase, it is possible to add specific additives to the composition in order to improve and / or optimize the process for manufacturing the materials, such as compatibilizers, for example. These additives facilitating the implementation of the process can be incorporated beforehand in one or the other of the polymeric phases, or with the fillers, or they can be incorporated independently.

- The process for preparing a porous composite material:

The process of the invention is based on the use of a sacrificial polymer phase in a melt process, allowing both plasticization, better fluidity of the material during processing and cohesion in the molten state, but also the creation of a controlled porosity. For example, an open porosity could be sought in order to reduce the density of the material while ensuring high thermal conductivity. The porosity can be controlled directly by the quantity of sacrificial material introduced or by a possible compression of the material after shaping and elimination of the sacrificial phase. It should be noted that the method according to the invention allows both short process times, typical of conventional plastics processing methods, such as extrusion, but also the use of steps requiring cohesion in the molten state such as extrusion calendering. It should also be emphasized that the ability of the mixture to be transformed is maintained after shaping, as long as no extraction or pyrolysis or graphitization has been carried out.

1. a) Mélangeage à chaud par voie fondue de la phase polymérique formant liant (A), des charges (B), et de la phase polymérique sacrificielle (C) de façon à obtenir un mélange,
2. b) Mise en forme du mélange,
3. c) Elimination de la phase polymérique sacrificielle.

This process comprises the following steps:

1. a) Hot melt mixing of the binder-forming polymer phase (A), of the fillers (B), and of the sacrificial polymer phase (C) so as to obtain a mixture,
2. b) Shaping of the mixture,
3. c) Elimination of the sacrificial polymeric phase.

Step a) can be implemented in a known manner in any type of equipment making it possible to homogenize the composition while heating it. Mention may in particular be made of an internal mixer or an extruder. Compared to the prior methods, the method of the invention has many advantages and in particular the mixing step is carried out without solvent. The binder-forming polymeric phase is homogeneously dispersed in the continuous sacrificial polymeric phase, or else it forms a co-continuous phase with the latter.

To facilitate obtaining a homogeneous mixture, it is for example possible to use the sacrificial polymer phase in the form of granules of average size in number greater than 1 mm.

The heating is controlled so as to bring the polymeric phases to fusion without decomposing the sacrificial phase or to a temperature at which the sacrificial phase decomposes very slowly (over a period of more than 1 hour). Advantageously, the heating in step a) is controlled to bring the mixture to a temperature at least 20 ° C. above the glass transition or melting temperature of the polymers of the polymeric phase forming binder.

The shaping step is adapted as a function of the final shape and of the dimensions that one wishes to confer on the object. The shaping can consist, for example, of one or more steps chosen from: extrusion, blowing, injection, molding, calendering, kneading and their combinations.

An advantage of the method of the invention lies in the possibility, when loads with a form factor are used, of orienting these loads. The creation of porosity in itself contributes to the orientation of these charges. Moreover, the passage through an extrusion die under selected pressure conditions makes it possible to confer orientation on such loads. Compression and / or calendering can also contribute to the orientation of loads. Such an orientation of charges in the porous composite material results in an asymmetry of the properties, and makes it possible to increase the properties of thermal conductivity or of electrical conductivity in one direction of the material.

The method of the invention also makes it possible to obtain objects of various shapes, self-supporting, and not only coverings attached to a support.

Preferably, the sacrificial polymeric phase is eliminated substantially without leaving any residue. This step can be carried out in a known manner by raising the temperature, for example in an oven. It can also be carried out by other means, such as for example by dissolving the sacrificial phase using a solvent.

In addition to the steps described above, the method of the invention may include other steps. In particular, according to one embodiment of the invention, it comprises one or more shaping steps at the end of step c), and in particular a cutting of the material to the desired dimensions, a compression which makes it possible to reduce porosity. The compression can for example be carried out by means of a plate press or by calendering. A possible crosslinking of the binder-forming phase is possible to optimize the mechanical properties and the cohesion of the composition if a subsequent transformation is not envisaged.

- The porous composite material

The porous composite material of the invention comprises at least one polymeric phase based on a polymer chosen from thermoplastic polymers, elastomers and elastomeric thermoplastics, and at least one filler chosen from thermal conductive charges and electrically conductive charges, the or the filler (s) representing at least 75%, advantageously at least 80% by mass relative to the total mass of the material. Advantageously, the filler (s) represent at least 60% by volume relative to the total volume of the material.

• 3 à 25 % d'au moins un polymère choisi parmi les polymères thermoplastiques, les élastomères et les thermoplastiques élastomères,
• 75 à 97 % d'au moins une charge choisie parmi les charges conductrices thermiques et les charges conductrices électriques,
• 0 à 5 % d'un ou plusieurs additifs ou de résidus de décomposition de la phase sacrificielle.

Advantageously, the porous composite material comprises, or better consists essentially of, by mass relative to the total mass of the material:

• 3 to 25% of at least one polymer chosen from thermoplastic polymers, elastomers and elastomeric thermoplastics,
• 75 to 97% of at least one load chosen from thermal conductive loads and electrically conductive loads,
• 0 to 5% of one or more additives or decomposition residues of the sacrificial phase.

• 3 à 20 % d'au moins un polymère choisi parmi les polymères thermoplastiques, les élastomères et les thermoplastiques élastomères,
• 80 à 97 % d'au moins une charge choisie parmi les charges conductrices thermiques et les charges conductrices électriques,
• 0 à 2 % d'un ou plusieurs additifs ou de résidus de décomposition de la phase sacrificielle.

Preferably, the porous composite material comprises, or better consists essentially of, by mass relative to the total mass of the material:

• 3 to 20% of at least one polymer chosen from thermoplastic polymers, elastomers and elastomeric thermoplastics,
• 80 to 97% of at least one load chosen from thermal conductive loads and electrically conductive loads,
• 0 to 2% of one or more additives or decomposition residues of the sacrificial phase.

• 4 à 10 % d'au moins un polymère choisi parmi les polymères thermoplastiques, les élastomères et les thermoplastiques élastomères,
• 90 à 96 % d'au moins une charge choisie parmi les charges conductrices thermiques et les charges conductrices électriques,
• 0 à 1 % d'un ou plusieurs additifs ou de résidus de décomposition de la phase sacrificielle.

Even more preferably, the porous composite material comprises, or better consists essentially of, by mass relative to the total mass of the material:

• 4 to 10% of at least one polymer chosen from thermoplastic polymers, elastomers and elastomeric thermoplastics,
• 90 to 96% of at least one load chosen from thermal conductive loads and electrically conductive loads,
• 0 to 1% of one or more additives or decomposition residues of the sacrificial phase.

• 3 à 25 % d'au moins un polymère choisi parmi : le polyacrylonitrile, les polyoléfines, les polymères halogénés, les polymères acryliques, les acrylates, les méthacrylates, les vinyl acétates, les polyéthers, les polyesters, les polyamides, les polymères aromatiques, l'acrylonitrile-butadiène hydrogéné, les copolymères d'éthylène et d'un acrylate d'alkyle, le polyisoprène, les caoutchoucs,
• 75 à 97 % d'au moins une charge choisie parmi : le nitrure d'aluminium, le nitrure de bore, le nitrure de magnésium et de silicium, le carbure de silicium, le diamant, et leurs mélanges,
• 0 à 5 % d'un ou plusieurs additifs ou de résidus de décomposition de la phase sacrificielle.

According to one embodiment of the invention, the porous composite material comprises, or better consists essentially of, by mass relative to the total mass of the material:

• 3 to 25% of at least one polymer chosen from: polyacrylonitrile, polyolefins, halogenated polymers, acrylic polymers, acrylates, methacrylates, vinyl acetates, polyethers, polyesters, polyamides, aromatic polymers, hydrogenated acrylonitrile-butadiene, copolymers of ethylene and of an alkyl acrylate, polyisoprene, rubbers,
• 75 to 97% of at least one filler chosen from: aluminum nitride, boron nitride, magnesium and silicon nitride, silicon carbide, diamond, and mixtures thereof,
• 0 to 5% of one or more additives or decomposition residues of the sacrificial phase.

• 3 à 20 % d'au moins un polymère choisi parmi : le polyacrylonitrile, les polyoléfines, les polymères halogénés, les polymères acryliques, les acrylates, les méthacrylates, les vinyl acétates, les polyéthers, les polyesters, les polyamides, les polymères aromatiques, l'acrylonitrile-butadiène hydrogéné, les copolymères d'éthylène et d'un acrylate d'alkyle, le polyisoprène, les caoutchoucs.
• 80 à 97 % d'au moins une charge choisie parmi : le nitrure d'aluminium, le nitrure de bore, le nitrure de magnésium et de silicium, le carbure de silicium, le diamant, et leurs mélanges,
• 0 à 2 % d'un ou plusieurs additifs ou de résidus de décomposition de la phase sacrificielle.

According to an advantageous embodiment of the invention, the porous composite material comprises, or better consists essentially of, by mass relative to the total mass of the material:

• 3 to 20% of at least one polymer chosen from: polyacrylonitrile, polyolefins, halogenated polymers, acrylic polymers, acrylates, methacrylates, vinyl acetates, polyethers, polyesters, polyamides, aromatic polymers, hydrogenated acrylonitrile-butadiene, copolymers of ethylene and of an alkyl acrylate, polyisoprene, rubbers.
• 80 to 97% of at least one filler chosen from: aluminum nitride, boron nitride, magnesium and silicon nitride, silicon carbide, diamond, and mixtures thereof,
• 0 to 2% of one or more additives or decomposition residues of the sacrificial phase.

• 4 à 10 % d'au moins un polymère choisi parmi : le polyacrylonitrile, les polyoléfines, les polymères halogénés, les polymères acryliques, les acrylates, les méthacrylates, les vinyl acétates, les polyéthers, les polyesters, les polyamides, les polymères aromatiques, l'acrylonitrile-butadiène hydrogéné, les copolymères d'éthylène et d'un acrylate d'alkyle, le polyisoprène, les caoutchoucs,
• 90 à 96 % d'au moins une charge choisie parmi : le nitrure d'aluminium, le nitrure de bore, le nitrure de magnésium et de silicium, le carbure de silicium, le diamant, et leurs mélanges,
• 0 à 1 % d'un ou plusieurs additifs ou de résidus de décomposition de la phase sacrificielle.

According to a preferred embodiment of the invention, the porous composite material comprises, or better consists essentially of, by mass relative to the total mass of the material:

• 4 to 10% of at least one polymer chosen from: polyacrylonitrile, polyolefins, halogenated polymers, acrylic polymers, acrylates, methacrylates, vinyl acetates, polyethers, polyesters, polyamides, aromatic polymers, hydrogenated acrylonitrile-butadiene, copolymers of ethylene and of an alkyl acrylate, polyisoprene, rubbers,
• 90 to 96% of at least one filler chosen from: aluminum nitride, boron nitride, magnesium and silicon nitride, silicon carbide, diamond, and mixtures thereof,
• 0 to 1% of one or more additives or decomposition residues of the sacrificial phase.

Advantageously, this material is obtained at the end of the process described above.

The material of the invention has a proportion of fillers greater than those known from the prior art for compositions based on polymers of the same nature. It therefore exhibits improved thermal conductivity and / or electrical conductivity properties compared to the compositions of the prior art. The porous composite material of the invention exhibits a porosity and a density which can be controlled. Indeed, several parameters of the process make it possible to modify these properties of the material: the proportions of the initial mixture of (A), (B), (C) and optionally, the shaping mode, a possible compression step. The porosity can thus be controlled in terms of size, morphology and quantity of the pores. Depending on the applications and the constraints associated with the use, one chooses to favor a more or less high density of the material. Extreme compression can achieve very low porosity.

By porous composite material is meant a material of which at least 1% by volume, advantageously at least 10% by volume, consists of pores.

Advantageously, the material of the invention has continuous porosity.

According to one embodiment of the invention, the porosity represents from 10 to 70% by volume relative to the total volume of the material, preferably from 20 to 60%.

The material is shaped according to the intended use, in particular in the form of sheets, films, but also sheaths, cables, coatings, granules, boxes.

Advantageously, the material of the invention is self-supporting.

Compared to the porous composite materials described in the prior art, the material of the invention has the advantage of not necessarily being in the form of a coating. Compared to the materials obtained by the solvent route, which can also be porous, the material of the invention has the advantage of being able to have various shapes, of considerable thickness. Indeed, by the solvent route, one has access to materials in the form of films of a few hundred microns of maximum thickness, while the materials of the invention can be of all shapes and of all dimensions. On the assumption that the material of the invention is in the form of a film, for example a coating film, advantageously, it is of a thickness greater than or equal to 250 μm, preferably greater than or equal to 500 μm, advantageously even greater or equal to 1 mm, even better, greater than or equal to 2.5 mm.

The material of the invention is advantageously characterized in that it has in all directions of space a thickness greater than or equal to 250 μm, preferably greater than or equal to 500 μm, advantageously still greater than or equal to 1 mm.

The materials of the invention exhibit an advantageous combination of properties: For example, it is possible to obtain by the process of the invention a material comprising a polymeric matrix based on a polymer chosen from thermoplastic polymers, elastomers and thermoplastic elastomers exhibiting at both a volume porosity greater than or equal to 40% and a thermal conductivity in at least one direction greater than or equal to 5W / mK

According to another variant of the invention, it is possible to obtain materials comprising a polymer matrix based on a polymer chosen from thermoplastic polymers, elastomers and elastomeric thermoplastics, thermal conductive fillers, and having thermal conductivity in at least one direction. greater than or equal to 15 W / mK

An advantage of the material of the invention over the materials of the prior art, in particular the crosslinked materials, is that it is convertible and can be recycled. One can in particular implement in step a) of the process described above a porous composite material according to the invention based on polymer and fillers, by adding a new sacrificial phase, optionally other polymers and fillers. additional, and thus proceed to a new cycle of transformation.

The targeted applications are different depending on the type of load that has been chosen.

In one embodiment, thermally conductive fillers are used. According to this embodiment, the material of the invention can be used in numerous applications such as: heat sink in electronic equipment (heat sink), automobile housings, housings of lamps, in particular of LEDs, encapsulation of electronic components, battery boxes, electrical cabinets, servers.

In another embodiment, electrically conductive charges are used. According to this embodiment, the material of the invention can be used in numerous applications such as: electric cables, coatings for electromagnetic shielding, anti-lightning, antistatic protection.

- The polymeric composition:

1. (A) une phase polymère transformable par voie fondue, avantageusement à base de polymères choisis parmi les polymères thermoplastiques, les élastomères et les thermoplastiques élastomères,
2. (B) une charge choisie parmi les charges conductrices thermiques et les charges conductrices électriques
3. (C) une phase polymérique sacrificielle,

les charges (B) représentant au moins 75 %, avantageusement au moins 80% en masse par rapport à la somme des masses du polymère (A) et des charges (B), la phase polymérique sacrificielle (C) représentant au moins 15 % en masse par rapport à la somme des masses de (A), (B) et (C).The polymeric composition is an intermediate composition of the process of the invention obtained at the end of steps a) or b) depending on whether it is still in the molten state or already shaped. It is a precursor of the porous composite material. This composition includes at least:

1. (A) a melt-convertible polymer phase, advantageously based on polymers chosen from thermoplastic polymers, elastomers and thermoplastic elastomers,
2. (B) a load chosen from thermal conductive loads and electrically conductive loads
3. (C) a sacrificial polymeric phase,

the fillers (B) representing at least 75%, advantageously at least 80% by mass relative to the sum of the masses of the polymer (A) and of the fillers (B), the sacrificial polymeric phase (C) representing at least 15% in mass with respect to the sum of the masses of (A), (B) and (C).

1. (A) 1 à 15 % de phase polymère à base de polymères choisis parmi les polymères thermoplastiques, les élastomères et les thermoplastiques élastomères,
2. (B) 35 à 70 % de charge(s) choisie(s) parmi les charges conductrices thermiques et les charges conductrices électriques
3. (C) 20 à 60 % de phase polymérique sacrificielle
4. (D) 0 à 3% d'additifs.

Advantageously, the polymeric composition comprises, by mass relative to the total mass of the composition:

1. (A) 1 to 15% of polymer phase based on polymers chosen from thermoplastic polymers, elastomers and thermoplastic elastomers,
2. (B) 35 to 70% of load (s) chosen from among thermal conductive loads and electrically conductive loads
3. (C) 20 to 60% sacrificial polymer phase
4. (D) 0 to 3% additives.

1. (A) 1 à 15 % de phase polymère à base de polymères choisis parmi les polymères thermoplastiques, les élastomères et les thermoplastiques élastomères,
2. (B) 35 à 70 % de charge(s) choisie(s) parmi les charges conductrices thermiques et les charges conductrices électriques
3. (C) 20 à 60 % de phase polymérique sacrificielle
4. (D) 0 à 3 % d'additifs.

Even more advantageously, the polymeric composition consists essentially, by mass relative to the total mass of the composition, of:

1. (A) 1 to 15% of polymer phase based on polymers chosen from thermoplastic polymers, elastomers and thermoplastic elastomers,
2. (B) 35 to 70% of load (s) chosen from among thermal conductive loads and electrically conductive loads
3. (C) 20 to 60% sacrificial polymer phase
4. (D) 0 to 3% additives.

This polymeric composition can be prepared and shaped directly into the form desired for use (film, case, etc.).

Alternatively, an embodiment is provided in which the composition is prepared (homogeneous mixture in the molten route of components (A), (B) and (C)) and put in the form of granules, for example. This composition is then easily reintroduced into the process of the invention in step a). This embodiment makes it possible to provide a ready-to-use composition which does not require dosage of the components and avoids handling errors linked to the introduction of the components into the mixer.

- Manufacturing process of a thermal conductive and / or electrically conductive porous carbon material:

According to one embodiment of the invention, the composite material obtained at the end of the process described above can also be transformed by applying a pyrolysis or graphitization treatment. In a known manner, such a treatment is carried out at a temperature greater than or equal to 500 ° C, respectively greater than or equal to 1000 ° C. For this, the choice of the polymeric phase forming the binder must have been adapted to allow this step. A carbonaceous material is thus obtained comprising a high quantity of thermal conductive or electrically conductive charges and endowed with controlled porosity and density.

Such a material can be used for the following applications: encapsulation of electronic components, battery boxes, electrical cabinets, servers.

Experimental part : I- Materials and methods : 1.1 Materials : Binder-forming polymer :

• PL 1 : polyacrylonitrile marketed by the company Ineos under the reference Barex 210 ®
• PL2: HNBR (hydrogenated acrylonitrile-butadiene) elastomer sold by the company Zeon Chemicals under the reference Zetpol 2010L ®

Sacrificial polymer :

• PS 1: polypropylene carbonate marketed by the company Novomer under the reference Polyol 211-10 ®
• PS 2: polypropylene carbonate marketed by the company Empower Materials under the reference QPAC40 ®

Thermal conductive load:

• C1 : Graphite commercialisé par la société Timcal sous la référence C-therm 001 ©
• C2 : Nitrure d'aluminium

Extrudeuse : Coperion ZSK18
Mélangeur interne : Scamex de 300ml

• C1: Graphite marketed by the company Timcal under the reference C-therm 001 ©
• C2: Aluminum nitride

Extruder: Coperion ZSK18
Internal mixer: 300ml Scamex

I.2. Test and characterization methods : Thermal conductivity :

The materials were characterized at room temperature and in-plane by the TPS thin plate hotdisk method following the NI IS022007-2: 2008-12 plastic standard.

Density :

To evaluate the density, the mass of the material was measured on a precision balance and the volume with a caliper, all at room temperature.

II. Polymeric compositions and composite materials:

In the composition tables, the “Before extraction” columns describe the proportions of the composition before step c) of elimination of the sacrificial phase, the “After extraction” columns describe the material obtained after step c).

II.1 Example 1 Formulation:

A mixture having the following composition was prepared: Table 1.1 Before extraction After extraction Composition %mass %volume %mass %volume PL1 13.2 17.4 19.9 29.1 PS1 13.8 16.5 0 0 PS2 19.8 23.8 0 0 C1 53.2 42.3 80.1 70.9

Preparation method: - Step a: Preparation of the composition and extrusion of a film of composite material

The composition was prepared using a twin screw extruder at 175 ° C. All the raw materials were directly injected into the extruder thanks to gravimetric dosers for powders and granules, and by an injection needle for liquids. The mass flow rates of each component were adjusted so as to obtain the composition described above.

- Step b: Formatting

The use of a gear pump following the twin-screw extruder made it possible to continuously extrude 2 mm thick films. The film was cut in the form of samples of dimension 5 cm x 5 cm.

- Step c: Elimination of the sacrificial phase

The film sample obtained above was subjected to a step of decomposition of the sacrificial phase in an oven in air at 230 ° C. for 20 min. The measurement of the mass difference before and after the heat treatment makes it possible to monitor and control the elimination of the polypropylene carbonate. 100% of the polypropylene carbonate initially incorporated in the mixture is decomposed and eliminated. A porous material is obtained consisting of polymer forming binder PL1 and filler C1 in the proportions of Table 1.1, and the porosity of which represents approximately 40% by volume relative to the total volume of the material.

- Step d: Compression

The porous material obtained in the previous step was compressed in a plate press at 80 ° C. and 80 bars to a thickness of 1.5 cm, which leads to a very significant reduction in porosity.

- Step e: Pyrolysis

The material is placed in an oven and subjected to a pyrolysis treatment at 600 ° C for 5 hours in order to pyrolyze the polyacrylonitrile binder.

Properties:

At each step, a sample was taken and the change in thermal conductivity was measured. The thermal conductivities obtained at the end of each process step are reported in Table 1.2. Table 1.2 Treatment Radial thermal conductivity (W / mK) Step a (mixing and extrusion) 16.6 Step c (elimination of the sacrificial phase) 12.5 Step d (compression) 16.9 Step e (pyrolysis) 17.1

II.1 Example 2 Formulation:

A mixture having the following composition was prepared: Table 2.1 Before extraction After extraction Composition % mass % volume % mass % volume PL2 3.7 5.9 6.1 11.3 PS1 25.1 30.7 0 0 PS2 13.5 16.6 0 0 C1 57.7 46.8 93.9 88.7

Preparation method: - Step a: Preparation of the composition and formation of a film of composite material

The composition was prepared using an internal mixer at 80 ° C. The binder polymer PL2 and the sacrificial polypropylene PS2 were introduced and mixed first in order to obtain a plasticized molten mixture. Then the mineral fillers C1 were gradually added with regular addition of the sacrificial polymer PS1 (preheating, to about 60 ° C, of the material may be necessary in order to reduce its viscosity and facilitate the addition) until a homogeneous mixture is obtained.

- Step b: Formatting

The mixture obtained above was then calendered in the form of a sheet 0.5 cm thick. The film obtained was cut in the form of samples of dimension 5 cm x 5 cm.

- Step c: Elimination of the sacrificial phase

The film sample obtained above was subjected to a step of decomposition of the sacrificial phase in an oven in air at 230 ° C. for 20 min. The measurement of the mass difference before and after the heat treatment makes it possible to monitor and control the elimination of the polypropylene carbonate. 100% of the polypropylene carbonate initially incorporated in the mixture is decomposed and eliminated. A volume expansion of the material is observed during this step. A porous material is obtained consisting of polymer forming binder PL2 and filler C1 in the proportions of Table 2.1.

- Step d: Compression

The mixture is compressed in a press at 80 ° C. and 50 bars to a film thickness of 0.5 cm in order to regain the original thickness. In fact, during decomposition, a slight swelling of the mixture is observed. The material after compression has a density of 0.844 g / cm ³ instead of 1.80 g / cm ³ theoretical (the theoretical density is calculated from the formulation and the density of each element). It is deduced from the measurement of the density that the material obtained has a porosity of 53% by volume relative to the total volume of the material.

Properties:

At the end of step d, the thermal conductivity of the material was measured in the radial direction and in the axial direction. The thermal conductivities obtained are reported in Table 2.2. Table 2.2 Meaning Thermal conductivity (W / mK) Radial 16.0 Axial 1.49

It can be seen that the material obtained combines several properties: high thermal conductivity, charge orientation and low density.

II.3 Example 3 Formulation:

A mixture having the following composition (“Before extraction” column) was prepared: Table 3.1 Before extraction After extraction Composition % mass % volume % mass % volume PL2 3.1 5.1 4.6 8.7 PS1 21.0 26.5 0 0 PS2 11.3 14.3 0 0 C1 64.6 54.1 95.4 91.3

Preparation method: - Step a: Preparation of the composition and formation of a film of composite material

The procedure was as in step a of Example 2.

- Step b: Formatting

The mixture obtained was then calendered in the form of a sheet 0.5 cm thick.

- Step c: Elimination of the sacrificial phase

The procedure was carried out as in step c of Example 2. A volume expansion of the material is observed during this step. A porous material is obtained consisting of polymer forming binder PL2 and filler C1 in the proportions of Table 3.1 (“After extraction” column).

- Step d: Compression

The mixture is compressed in a press at 80 ° C. and 50 bars to a film thickness of 0.5 cm in order to regain the original thickness. In fact, during decomposition, a slight swelling of the mixture is observed. The material after compression has a density of 1.05 g / cm ³ instead of the theoretical 1.82 g / cm ^3. It is deduced from the measurement of the density that the material obtained has a porosity of 42% by volume relative to the total volume of the material.

Properties:

At the end of step d, the thermal conductivity of the material was measured in the radial direction and in the axial direction. The thermal conductivities obtained are reported in Table 3.2. Table 3.2 Meaning Thermal conductivity (W / mK) Radial 22.4 Axial 1.55

It can be seen that the material obtained combines several properties: high thermal conductivity, orientation of the charges as well as low density.

II.4 Example 4 Formulation:

A mixture having the following composition (“Before extraction” column) was prepared: Table 4.1 Before extraction After extraction Composition % mass % volume % mass % volume PL2 4.2 9.0 5.0 15.0 PS1 7.7 20.0 0 0 PS2 7.6 20.0 0 0 C2 80.5 51.0 95.0 85.0

Preparation method: - Step a: Preparation of the composition and formation of a film of composite material

The procedure was as in step a of Example 2.

- Step b: Formatting

The mixture obtained was then calendered in the form of a sheet 1 cm thick.

- Step c: Elimination of the sacrificial phase

The procedure was as in step c of Example 2. No volume expansion of the material during this step is to be noted. A porous material is obtained consisting of polymer forming binder PL2 and of filler C2 in the proportions of Table 3.1 (“After extraction” column).

- Step d: Compression

The mixture is compressed in a press at 80 ° C. to a film thickness of 1 cm in order to ensure the original thickness even if no swelling of the mixture is observed.

Claims (15)

1. Process for the preparation of a porous composite material comprising at least (A) a binder-forming polymeric phase and (B) one or more fillers chosen from:

   thermally conductive fillers exhibiting a thermal conductivity of greater than or equal to 5 W/mK and electrically conductive fillers exhibiting a resistivity of less than or equal to 0.1 ohm.cm,

   the fillers (B) representing at least 75%, advantageously at least 80%, by weight, with respect to the sum of the weights of the polymeric phase (A) and of the fillers (B), this process comprising the following stages:

   a) hot mixing, by the molten route, the polymeric phase (A), the fillers (B) and a sacrificial polymeric phase (C), so as to obtain a mixture,

   b) shaping the mixture,

   c) removing the sacrificial polymeric phase,

   and the sacrificial polymeric phase (C) represents at least 15% by weight of the total weight of the mixture of stage a),

   the porous composite material comprising, by weight, with respect to the total weight of the material, from 0% to 5% of one or more decomposition residues from the sacrificial phase.
2. Process according to Claim 1, in which the sacrificial polymeric phase (C) represents from 20% to 80% by weight of the total weight of the mixture of stage a).
3. Process according to either one of the preceding claims, in which stage a) is carried out in an internal mixer or in an extruder.
4. Process according to any one of the preceding claims, in which stage c) is carried out by decomposition by the thermal route of the sacrificial polymeric phase.
5. Process according to Claim 4, in which the sacrificial polymeric phase is based on at least one polymer chosen from polyalkene carbonates, preferably from polyethylene carbonates and polypropylene carbonates.
6. Process according to any one of the preceding claims, in which the binder-forming polymeric phase is based on at least one polymer chosen from: thermoplastics, elastomers, thermoplastic elastomers, advantageously from: polyacrylonitrile, polyolefins, halogenated polymers, acrylic polymers, acrylates, methacrylates, vinyl acetates, polyethers, polyesters, polyamides, aromatic polymers, hydrogenated acrylonitrile/butadiene, copolymers of ethylene and of an alkyl acrylate, polyisoprene or rubbers.
7. Process according to any one of the preceding claims, in which the fillers are chosen from: aluminium nitride, boron nitride, magnesium silicon nitride, silicon carbide, diamond, and their mixtures.
8. Process according to any one of Claims 1 to 6, in which the fillers are chosen from: graphite, graphene, carbon nanotubes (CNTs), carbon black, metal fillers, such as aluminium, copper or silver, and their mixtures.
9. Process according to any one of the preceding claims, in which stage b) comprises a fashioning in the film form.
10. Process according to any one of the preceding claims, which additionally comprises, on conclusion of stage c), a compression stage d).
11. Porous composite material capable of being obtained by the process according to any one of Claims 1 to 10, which exhibits the following composition, by weight, with respect to the total weight of the material:

    • from 3% to 25% of at least one polymer chosen from thermoplastic polymers, elastomers and thermoplastic elastomers,

    • from 75% to 97% of at least one filler chosen from thermally conductive fillers exhibiting a thermal conductivity of greater than or equal to 5 W/mK and electrically conductive fillers exhibiting a resistivity of less than or equal to 0.1 ohm.cm,

    • from 0% to 5% of one or more additives or decomposition residues from the sacrificial phase.
12. Porous composite material according to Claim 11, which is chosen from a self-supported material and a coating with a thickness of greater than or equal to 250 µm.
13. Material capable of being obtained by the process according to Claim 10, comprising a polymeric matrix, based on polymer chosen from thermoplastic polymers, elastomers and thermoplastic elastomers, and thermally conductive fillers and exhibiting a thermal conductivity in at least one direction of greater than or equal to 15 W/m.K.
14. Polymeric composition capable of being obtained on conclusion of stage a) or of stage b) of the process according to any one of Claims 1 to 9, this composition comprising at least:

    (A) a polymeric phase based on polymers chosen from thermoplastic polymers, elastomers and thermoplastic elastomers,

    (B) one or more fillers chosen from thermally conductive fillers exhibiting a thermal conductivity of greater than or equal to 5 W/mK and electrically conductive fillers exhibiting a resistivity of less than or equal to 0.1 ohm.cm,

    (C) a sacrificial polymeric phase,

    the filler or fillers (B) representing at least 75%, advantageously at least 80%, by weight, with respect to the sum of the weights of the polymer (A) and of the fillers (B), the sacrificial polymeric phase (C) representing at least 15% by weight, with respect to the sum of the weights of (A), (B) and (C).
15. Process for the manufacture of a thermally conductive and/or electrically conductive porous carbon-based material, this process comprising the implementation of the process according to any one of Claims 1 to 10 and additionally comprising, on conclusion of this process, at least one stage e) of pyrolysis or of graphitization.